A wireless device in a wireless communications network typically employs different operational modes to reduce energy consumption when possible. For example, when a wireless device's receiver is not actively receiving user data from the network, the device may switch to an operational mode that maintains the device's receiver in a so-called “off” or “sleep” state. The device's receiver consumes less energy in this state, but cannot listen for or otherwise detect connection request (e.g., page or wake-up) signals requesting the device to connect to the network. Accordingly, to detect these connection request signals, the device may periodically switch back to a normal operational mode in which the receiver is “on” or “awake.”
Although the device consumes less energy using this conventional sleep technique than if its receiver had remained awake constantly, the device still consumes a considerable amount of energy in periodically waking up its receiver. In addition, the fraction of time the receiver actually receives a connection request is typically very small, which means that most of the time the energy used during the wake-up period is wasted.
The considerable, wasteful energy consumption of the sleep technique prohibits its application in the context of Machine Type Communications (MTC) (also referred to as Machine-to-Machine, M2M, communications), where MTC devices must consume significantly less energy than other wireless device types. MTC devices must therefore resort to other energy consumption reduction techniques.
One such technique exploits the high signal strength typical of a dense MTC network. According to this technique, an MTC device employs two receivers, including a wake-up receiver and a conventional receiver. The device's wake-up receiver has a worse sensitivity than the device's conventional receiver. The wake-up receiver's sensitivity is worse because the wake-up receiver amplifies received signals less than the conventional receiver, meaning that the received signals must arrive at the wake-up receiver with higher signal strength than signals arriving at the conventional receiver in order to be detected. Generally, it is desirable for a receiver to be capable of detecting signals with as low of signal strength as possible. Looking at this receiver characteristic alone, therefore, the wake-up receiver is considered to have worse receiver sensitivity than the conventional receiver.
Despite the worse sensitivity of the wake-up receiver, the receiver is still able to receive a network connection request, since such a request has a high signal strength in the dense network. Moreover, the wake-up receiver consumes less energy than the conventional receiver (e.g., because the wake-up receiver amplifies received signals less). The device exploits these characteristics of the wake-up receiver and conventional receiver in order to reduce energy consumption. Specifically, the device maintains the energy-efficient wake-up receiver in a constant active state in order to listen for network connection requests, while maintaining the conventional receiver in a constant sleep state. Only when the wake-up receiver detects a network connection request does the receiver wake up the conventional receiver, whereupon the conventional receiver proceeds to receive data from the network.
Known techniques for reducing wireless device energy consumption therefore prove to have limited advantages and limited application scope. Some techniques (e.g., conventional sleep techniques) still consume and waste a considerable amount of energy, and do not reduce energy consumption enough for certain applications (e.g., MTC applications). Other techniques (e.g., wake-up receiver techniques) better reduce energy consumption, but do not accommodate applications characterized by relatively low signal strength (e.g., sparse MTC network applications or mobile communications applications).